Based on the three-book series from The Vampire Diaries author L.J. Smith, Secret Circle follows Cassie Blake (Robertson), a young witch who moves back to her mother's mystical hometown. Unaware of her powers at first, Cassie may be the key that will unlock the battle of good versus evil.
Robertson will be free to join Circle unless Life Unexpected gets picked up for a third season, which looks unlikely.
Diaries ' Kevin Williamson will executive produce.